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Unread 09-05-2014, 11:02 PM   #1
Shady at Best
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Ditra-Heat will not stick?

I installed 60 feet of ditra Thursday am. I used some maipei modified thinset that a member here recommended. I lifted a corner of each sheet to confirm good coverage.
I went back today, about 20 hours later. I was cleaning a few spots where thinset had oozed up between the sheets. I was vacuuming up the debris when all of the sudden the ditra released and peeled right up. The fleece was basically clean, but moist. Almost like the ditra was sweating.
All the videos that I have seen show them laying the ditra and then tiling over it the same day. I wonder if that is the problem. Or if it was me walking on it but I didn't step on every square inch.

So what's the deal with this stuff. It's the first time that I have used ditra on plywood. The thinset grabbed the plywood with no problem.
Is it possible to set ditra, let it dry for a day and then walk on it?
Look how clean this felt is. There was complete adhesion.

Oh and the thinset was about as runny as a milkshake on some sheets and a little thicker on some. I wet the plywood with a damp sponge

This pic was taken 20 hours after being set. This is not a pic of the installation
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Last edited by Shady at Best; 09-06-2014 at 01:29 PM.
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Unread 09-06-2014, 02:55 AM   #2
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Quote:
Originally Posted by Travis
I lifted a corner of each sheet to confirm good coverage.
Here's the problem I have with your statement after looking at your picture: There appears to be very little or no thinset on the fleece you have there. That's the biggest red flag I see, no transfer of thinset into the fleece. If the thinset was properly mixed and applied, it would be smashed into the fleece such that you wouldn't see that imprint.

1. How long did you have the thinset on the floor before you covered it?

2. How many square feet of thinset did you comb out before covering it?

3. Specifically what thinset did you use?

4. What size trowel did you use?

5. Did you have a fan running in the room?

6. After setting the Ditra over the thinset, did you use a wood float or some other tool to force the Ditra into the thinset?

It looks like the thinset was too dry when you spread it, or you let it set too long before covering it. Basically, it just shouldn't look like it does in your picture.
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Unread 09-06-2014, 03:26 AM   #3
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Just a guess but I'm thinking too wet and ruined the bonding properties of the thinset.
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Unread 09-06-2014, 04:16 AM   #4
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Could be a lot things, but one that does that is foot traffic from somebody working over it at a crucial stage in thinset curing, can be hours after you set it. Overwet thinset will be more susceptible to curing failures.
I use sheets of plywood if I have to walk over it more than a couple times right at installation. The standard bond is very low, maybe 50 psi, so it's not made to be picked at or intentionally peeled at the edges (uncoupling membrane). You should still be able to vacuum it though of course.
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Unread 09-06-2014, 04:45 AM   #5
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I must chime in on this`un!! I`ve been putt`n Ditra down for ???15 years and the last two jobs I`ve done and needed to remove a small section /went to far in the doorway by 4 inches or so or needed to remove to allow the carpenters to attach a base plate for a spiral staircase and I experienced the same as Shady! ??? Although I use regular Ditra and he used Ditra heat mat prolly same fleece ?

My first time I gasped ! and reasoned must nota pressed hard enough ? second time I know there was coverage cause I check all da time as I`m spreading and I had to remove a piece exactly where I checked coverage 20 or so hours earlier and I experienced the same results/not sticking as Shady?? And looked with magnifying glass and saw definite impression from all the little holes of the fleece in the thinset on the floor but clean as a whistle on the Ditra ? . I`m definitely calling Schluter now!!! Or if any of the Reps are secretly watching ? Shhhh!! and we know they are ! :-) Did they change the fleece ??? I always use 254 to set Ditra but the last few times had none and used Versabond . Once over wood and next over concrete both stuck like mad to the substrate but same thing as pic above! Gona hold off on putting any more down till I get an answer ! Maybe I`ll try Stratamat for once!
By the way I`m the 3 largest purchaser of Ditra in my lil ole region at my supplier. So put down plenty.
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Unread 09-06-2014, 05:58 AM   #6
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Travis, what we have found is that fast setting type thinsets work best if you're going to be on the membrane at all.

Our everyday thinset of Tec FULLFLEX has had similar results.

The ditra heat is I believe made from polyethylene which is a bit stiffer than what ditra is made from.

Couple things to check/do
1) Date code on thinset.
2) Need good 1/4"x1/4" trowel
3) Checking moisture content of substrate prior to installing the membrane May not hurt.
4) unrolling membrane to allow it to relax or re-rolling the opposite direction may help to do prior to install....
5) acclimating materials on job site days before install always helps.

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Unread 09-06-2014, 05:59 AM   #7
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looks like a small v-notch trowel was used to install Ditra heat....That said, they require a 1/4x1/4 for the installation of mat to substrate for this product.
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Unread 09-06-2014, 10:48 AM   #8
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Seems like all the other questions are asked but this: Which specific modified Mapei thinset did you use?

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Unread 09-06-2014, 10:55 AM   #9
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I think the trowel size is one problem and I wonder what the answer to Kurt's question is too.
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Unread 09-06-2014, 12:44 PM   #10
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Keep in mind that thinset does NOT stick to Ditra! You get a bond because, when the thinset is mixed properly and the fleece properly embedded, the thinset surrounds the fleece. When it cures, it then locks the rest of the membrane in place. Yes, a modified will maybe stick a little bit to the fleece, but it is by no means the primary means of adhesion.

It looks to me (it's hard to tell from the pictures) that either the thinset skinned over too much or was not fluid enough in the first place to 'flow' around the fleece. The specification for any of these fleece based membranes is 50psi once fully cured and properly installed (Ditra usually tests at 75+psi, or 50% above the minimum spec), and keep in mind that while a lot happens overnight, the specification says 'full cure' is at 28-days. IOW, it can be fairly easy to peel back the membrane for maybe days, especially if you do not have the thinset surrounding the fleece. If it was, when you peeled it back, you would have torn the fleece off from the back of the membrane.
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Unread 09-06-2014, 01:25 PM   #11
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I used a 1/4x1/4 v notched trowel.
I set 15 feet/ one sheet at a time only spread out enough for one sheet, it abosolutely did not skin over.

I smoothed it out with a wooden trowel.

The pic posted was it lifting up after 20 hours, not a pic of wet thinset showing adhesion. My hands were too messy to want to bust out the (NEW) camera during install

Lou, exact same thing here. I rinsed the ditra felt side off after I pulled it up and water beaded up like it was water proof.

After I pulled it all up I scraped and ground the dried thinset off the plywood.
I picked up some versaset and installed it again. This time I pulled each sheet back up to check coverage. I also back buttered a few sheets.

The thinset might have been a bit runny if anything. It would barely hold a peak once troweled. I doubt it did anything negative to the thinset. The area that were troweled out but never got ditra on it were rock hard and stuck. I tried scraping it up with a 5 inch scraper and it didnt work.
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Last edited by Shady at Best; 09-06-2014 at 01:31 PM.
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Unread 09-06-2014, 01:52 PM   #12
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Travis, the thread title says Ditra, but it appears you're using Ditra-Heat. Is that correct?

I see that you used a 1/4" vee notched trowel, rather than the 1/4" square notch recommended by Schluter for Ditra-Heat. That also correct?

Trying to get an outside reading on this "issue."

[Edit]

Presuming the above to be both true and accurate, this is what I've learned from a reliable source:

The DITRA-HEAT is a little different to install from DITRA because the (DITRA-HEAT) matting is a bit stiffer. That's why they (Schluter) recommend the larger 1/4" x 1/4" square-notched trowel. The fleece is a little different too, but they haven't seen it behave differently. Best guess is that you just got too much tension with the shop vac and the weak link at the time was the mortar/fleece interface.

While some extra thin-set mortar might have helped to really engage the fleece, at the end of the day 20 hours just isn't enough time for the mortar to gain enough strength to hold the fleece and tear from the membrane. Herr Schluter does bond strength evaluations from time-to-time or builds mock ups and they don't see the fleece remain on the floor or pull up the bond coat on day 2 or 3.

If it's possible that you still have access to that membrane installation a full week from installation, I'd be interested to know if you find the bond quite different then or if you still see the same thing you saw after only 20 hours cure time.

We pretty regularly hear the same sort of concern from people using Kerdi for the first time and trying to peel it off the wall the next day. While it'll come right off rather easily the next day, after a week it's a very different story.

Keep also in mind that the bonding requirement for either of those products is a final shear bond of only 50psi and no bond testing is done at less than the full 7-day cure. No pull bond testing is done or required.

My opinion; worth price charged.
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Unread 09-06-2014, 03:13 PM   #13
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It is ditra heat*

Schluters site
Q. What size trowel should I use to install Schluter-DITRA?*A. A 1/4" x 3/16" or 5/16" x 5/16" V-notched trowel is recommended.* Mix your thin-set mortar to a fairly fluid consistency (but still able to hold a notch) and solidly embed the Schluter-DITRA into the fresh mortar with a float or scre There isn't any difference in installation according to schluter.
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Unread 09-06-2014, 04:38 PM   #14
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Pour liquid wax onto your nice woven woolen suit verses press a block of solid wax there. The liquid wax, once it solidifies will have a tenacious grip on the fibers. The solid block won't. Thinset and 'sticking' with Ditra don't equate...the only way Ditra, Kerdi, Stata_Mat, Hydro-Ban sheet and any other fleece covered membrane designed to be applied with thinset, relies on the thinset fully encasing and coating the fibers, not sticking to them. If you do not get the mix right, or use an acceptable product, or install it properly, your results will be less than optimum. You don't want thinset ON the fleece, you want it IN-BETWEEN the fleece fibers...if you do that, once the thinset cures, it is well locked in place. The thinset needs to flow when you embed the membrane into the thinset. Done properly, the thinset will reach the solid membrane to the bottom of the fleece, fully coating the fibers so an attachment is certain.

Spreading 15' of thinset out a meter wide before covering it with the membrane, is, I think, asking too much. Keep the membrane loosely rolled up, spread a few feet of thinset, embed it, then spread some more thinset and continue, and I think your results would have be significantly different.
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Unread 09-06-2014, 04:53 PM   #15
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Quote:
Originally Posted by Travis
Schluters site
Q. What size trowel should I use to install Schluter-DITRA?*A. A 1/4" x 3/16" or 5/16" x 5/16" V-notched trowel is recommended.* Mix your thin-set mortar to a fairly fluid consistency (but still able to hold a notch) and solidly embed the Schluter-DITRA into the fresh mortar with a float or scre There isn't any difference in installation according to schluter.
That recommendation is for Ditra, Travis, rather than DitraHeat. That's what I was trying to sort out above.

If you'll download the Installation Handbook for Ditra-Heat from the Schluter site you'll see the difference in the recommendations.
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